The goal of this project is to provide to the nuclear medicine community a simple, reliable, safe and effective radiopharmaceutical for scintigraphic visualization of deep vein thrombi and pulmonary emboli. Such a radiopharmaceutical, consisting of suitably labeled fibrinogen, would be useful in the non-invasive diagnosis of thromboembolic disease. Specifically, the proposal envisions the following objectives: (1) To develop and compare methods to effect stable binding between fibrinogen and radionuclides of the metals technetium, gallium, and indium. (2) To determine the physicochemical and biologic properties of the labeled fibrinogen to select the optimum preparations. (3) To investigate the utility of these preparations for imaging induced deep vein thrombi and pulmonary emboli in experimental animals. To accomplish these objectives the synthesis and use of bifunctional chelating agents will be studied for binding the radiometals to the fibrinogen by an indirect mechanism. The labeled protein will be subjected to an extensive series of screening tests to ascertain stability, structural integrity, and biologic activity. The optimum preparations will be studied in animal models of venous thrombosis and pulmonary embolism. Based on these data, the potential applicability of the radiolabeled fibrinogen for clinical use will be assessed.